1. Field of the Invention
The present invention relates generally to injection devices for use with an external infusion system for subcutaneous delivery of a selected medication or other therapeutic fluid to a patient, and more particularly to an improved subcutaneous injection set of the type having a soft or flexible cannula, in combination with means for reducing and/or eliminating undesired crimping or kinking of the soft cannula during transcutaneous placement.
Subcutaneous injection devices are generally known in the art for use in the administration of a selected medication or other therapeutic fluid to a desired subcutaneous site located beneath the skin of a patient. Such injection devices or sets commonly include a tubular cannula or catheter which is supported by and protrudes from a compact housing adapted to receive the infusion fluid via a delivery to be connected suitably to other components of the fluid infusion system.
An insertion needle is normally provided to extend through a lumen formed in the cannula and thereby provide a rigid backstop structure having a sharp-tipped end to facilitate transcutaneous placement of the cannula. The insertion needle is thereafter withdrawn to leave the cannula in place for subcutaneous fluid infusion to the patient. A preferred subcutaneous injection set of this general type is described and claimed in U.S. Pat. No. 4,755,173, to Konopka et al., and in U.S. Pat. No. 5,176,662, to Bartholomew et al., both of which are hereby incorporated herein by reference.
For optimum patient comfort during use, the cannula is desirably constructed with a high degree of softness and flexibility. However, a soft and flexible cannula can on occasion become crimped or kinked during the insertion process, resulting in obstruction of the lumen of the cannula and resultant inability to deliver the desired medication to the patient. More specifically, during the transcutaneous insertion step, substantial longitudinal force is applied to the cannula as the insertion needle is passed through the patient's skin.
This longitudinal force can sometimes cause the soft cannula to displace or slip longitudinally on the insertion needle, resulting in incomplete cannula insertion and sufficient kinking to obstruct the lumen of the cannula. In the past, this problem has been addressed primarily by increasing the stiffness of the cannula, by means of increased wall thickness or variations in the cannula material to resist crimping during the insertion step. Unfortunately, these prior approaches effectively reduce the softness and flexibility of the cannula, and thereby compromise patient comfort.
There exists, therefore, a significant need for further improvements in subcutaneous injection sets and the like, particularly with respect to providing a cannula with a high degree of softness and flexibility, and wherein the soft cannula can be transcutaneously placed in a reliable manner substantially without crimping or kinking. The present invention fulfills these needs and provides further related advantages without incurring any substantial relative disadvantage.